The corals of Varadero have endured five hundred years of human conflict, but they may not survive Colombia’s fragile peace.

Valeria Pizarro releases air from her vest and breathes from her scuba regulator as she sinks into water the color of pea soup. Though the sea floor lies only a few meters below, she can’t see it. Sediment and algae give the water a brownish-green hue. Through the murky gloom, she can’t even make out the shape of her dive fins. She is on the hunt for corals, but she knows these fickle creatures prefer pristine waters and optimum conditions; her hopes aren’t high.

It’s 2013, and Pizarro, a Colombian biologist specializing in marine coastal ecosystems, is diving at the mouth of Cartagena Bay, one of the most polluted in all of South America. It’s busy, crowded and filthy, one of the oldest seaports in the hemisphere. Its waters are turbulent from the constant traffic of massive freighters. Visible in satellite photos, the plume of the discharge from the Canal del Dique spills into the bay leaving a brownish smudge that fans out into the brilliant blue of the Caribbean. It’s the last place you’d expect to find corals.